1. Field of the Invention
The present invention generally relates to a burner for use in a furnace and more particularly to a gas fired burner useful in steam producing or waste heat boilers.
2. Description of the Related Art
Gas burners for use in steam producing boilers that use air as a combustion oxidant typically involve highly turbulent and relatively high pressure drop designs which mix the fuel and air in the furnace section of the boiler. The flame envelope produced by such burners, whether they are arranged singly or in a multiple array, fills the open boiler furnace. Examples of known boilers that may be equipped with burners having the described operating characteristics are disclosed in the publication Steam: its generation and use, 40th ed., 1992, at pages 25-7 to 25-9, published by The Babcock & Wilcox Company.
Waste heat recovery boilers, also known as heat recovery steam generators, can utilize a duct burner design to boost the amount of heat available to the boiler. Typically, burners of such a design are placed in an open duct and are used to heat air or gases in the duct. Unlike the highly turbulent burners employed in above-referenced steam producing boilers, duct burners operate at higher excess air levels. A known waste heat recovery boiler design is depicted and described in the aforementioned Babcock & Wilcox publication at page 31-3.
The burner of the present invention, which has been termed a distributive integral gas burner (DIGB), has been developed to combine certain desirable features of the more conventional turbulent burners with those of duct burners. One of the objectives of the present invention has been to provide a burner with relatively low air side pressure drop while maintaining high burner efficiency with low excess air. Included among the benefits anticipated with such a burner are the ability to perform burner firing in narrower furnace confines, to reduce the power consumption of forced draft fans used with the boiler, to obtain reduced NO.sub.x emissions and to increase boiler steam ratings within a given boiler footprint. In order to achieve such benefits, the present invention utilizes a vertical fuel manifold which is placed between two air foils that define a vertically elongated venturi throat therebetween. Another aspect of the present invention, also aimed at the achievement of the enumerated benefits, is that it includes air foils which may have perforations to allow a secondary gas to be supplied behind the air foils and injected through the perforations and into the flame for reducing NO.sub.x production.
U.S. Pat. No. 244,746 discloses a plurality of transversely elongated rectangular ducts which alternately carry fuel and air and together form a horizontally elongated gas burner. The patent does not indicate that air foils should be provided between the alternating air and fuel passages or that perforations should be provided for admitting a secondary gas.
U.S. Pat. No. 741,465 employs curved tubular passages for directing a flame.
U.S. Pat. No. 1,911,117 discloses circular gas jets having a venturi structure downstream of the jets.
U.S. Pat. Nos. 1,950,046 and 1,99417 describe the use of air foil structures in a gas burner; however, elongated passages bounded by air foils to form a venturi are not disclosed in either of these patents.
U.S. Pat. No. 3,219,096 describes a structure having elongated passages, but the passages are provided for combining different gaseous fuels for combustion. The described structure does not employ elongated throats between adjacent air foils.
U.S. Pat. No. 4,009,989 discloses elongated throat channels for a fuel plus air mixture; however, air foils are absent from the structure.
U.S. Pat. No. 5,102,329 utilizes a gas manifold and U.S. Pat. No. 5,139,414 discloses a burner with primary and secondary combustion chambers.